The present invention relates to vehicle presence detection systems and, more particularly, to a detection system wherein presence signals are passively detected. In its broadest sense, the invention relates to detecting the presence of any object capable of varying light rays emanating therefrom in contrast to the ambient light conditions.
The prior art for vehicle presence systems generally utilize reflected signals, such as in radar systems, for detecting the presence of a vehicle and also the distance relative to the monitoring vehicle. These systems usually require a signal generator in the host vehicle which transmits and directs a suitable scanning signal along one or more lanes of a roadway, and a receiver for picking up the reflected signal from a nearby vehicle struck by the beam of the transmitted signal. These systems are very complicated and require complex electronic circuits, components and microprocessors.
In U.S. Pat. No. 4,258,351, a passive system is disclosed for detecting the presence of vehicles utilizing the change in brightness when a vehicle moves across a designated targeted area on a roadway. While this system may be efficient in use upon the roof of a building, it depends upon the accurate angularity and distance of a detecting device from the target area. The standardized device would not be suitable for use in a moving host vehicle whereby targets to-be-sensed are in continuous motion and at variable distances and angles relative to a target vehicle. The specific sensing device utilized in the patented system is devised to be insensitive to orientation of a target vehicle as to distance and to the relative angularity between the host vehicle and the roadway, or of positioning of one or more target vehicles.
In U.S. Pat. No. 4,433,325, a similar system is disclosed wherein a camera is mounted for surveillance upon a measured pole and has photocells therein angularly related to target points on a roadway.
The space monitoring system disclosed in U.S. Pat. No. 3,972,021 requires detecting devices to be mounted on a plurality of traffic light posts and therefore use in a moving vehicle is not feasible. Furthermore, the patented system is very complex with respect to the details incorporated in the detecting devices. The system relies on the analysis of measurements of a signal phase and amplitude and their variations with respect to the presence and/or motion of objects within a field of detection. A passive electro-optical device is disclosed for use in a rangefinding system in U.S. Pat. No. 4,009,960.
The present invention has many advantages over the art, most notably the POS system uses inexpensive commercially available components and the small size of the POS tube(s) requires a minimum of space for installation, and may permit a variety of mounting locations which would otherwise be impractical for larger units used in the other systems. The POS system is a single unit relying on passively reflected light in order to function while other systems require both a transmitter and receiver of some kind. Active systems such as radar, infrared, ultrasonic, etc. require transmitters and receivers which are relatively expensive to manufacture and are complex in construction. They also require careful calibration to function properly and may require periodic recalibration due to loss of accuracy from road vibrations, etc.
Other advantages will become apparent since the other systems previously mentioned have limited applications while the POS system is adaptable to a wide variety of uses. Other, active systems require electrical energy to power a transmitter and receiver whereas the POS system requires a minimal amount of electrical energy to perform its functions and may act more like a switching device. Wide-spread use of ground level radar or microwave transmissions may pose possible and unforeseen long-term health hazards for the public. The POS system offers simplified installation since complex wiring is not required, and the small physical size of the POS system contributes to ease of installation. The POS system has no moving parts to wear out and affect accuracy. It does not need complex electronic components thereby reducing the possibility of component related malfunctions. Finally, the POS system does not cause interference with police radar, citizen's radar detectors, remote control garage door openers or other devices utilizing microwaves for operation.
Therefore, it is the principal object of the invention to detect the presence or absence of moving objects, such as vehicles, on a roadway in a manner which is efficient, simple and provides highly credible information for the operator of the vehicle.
It is another object of the invention to utilize a passive object detection system in a vehicle cruise control system, thereby effecting credible control of the vehicle under conditions of functional visibility.
In accomplishing the object of the present invention, a Passive Optical Sensor, herinafter referred to as "POS", is devised to react to a change in the intensity of light passively reflected from its field of surveillance in response to the sudden presence or absence of an object within its field of surveillance.
Monitoring the field of surveillance is accomplished using a single photosensitive device or an array of such devices within tube structures arranged to be directed at one or more areas of surveillance. The devices may be arranged in a single linear array or multiple arrays and be monitored individually or in cell-pairs for voltage or current flucturations. These fluctuations are interpreted as indicating the presence of an object such as a vehicle, the relative motion of the vehicle and its direction of movement for use either to alert the driver or to automatically control his own vehicle accordingly. The photosensitive devices may include photoresistive photocells, such as the silicon dioxide or gallium arsenide types, or any PV cells made by stacking different PV materials, as known in the art, or phototransistors, because of their faster response times or any other light sensitive device.
These and other objects of the invention will become apparent after reviewing the following description taken in conjunction with the accompanying drawings.